System for preheating and transporting viscous fuel and the like



W. J. TRABILCY SYSTEM FOR PREHEATING AND TRANSPORTING VISCOUS FUEL AND THE LIKE Filed April 24 1957 Oct. 20, 1959 INVENTOR Mama 4/ Tana/4c) ATTORNEY 6 Patented SYSTEM FOR PREHEATIN G AND TRANSPORTIN G VISCOUS FUEL AND THE LIKE This invention relates to a system for transporting a viscous liquid such as fuel oil from a receptacle such as a storage tank to a device where the liquid is used such as an oil burner and is particularly concerned with a novel single supply line system having special heating and flow control arrangements.

Prior to the invention the conventional practice was to draw fuel oil out of a storage tank into a supply line and pump it in an amount considerably in excess of the needs of the associated burner or burners through the electrically heated pipe of the supply line to the burner or burners and then return the excess heated oil from the burner location through an electrically heated return line which extended into the tank and terminated in the body of tank oil near the open suction end of the supply line which was near the bottom of the tank. It was believed that such a system involving return of hot excess oil into the tank through a return line was essential to provide a mass of pumpable oil within the tank at the suction end of the supply line. The system of the present invention does away entirely with the need for a return line and all of the attendant extra parts and expense and contemplates drawing fuel oil out of the storage tank only in the amount and at such a rate as to satisfy the burning rate of the oil burner or burners actually using oil. This means that less power is wasted pumping oil around a system as was needed in the old two line system and smaller pumps and pipes are used, the pipe costs are halved and the cost of electrically heating the pipes is halved. Upkeep is simpler and less costly, and the single line system of the invention, besides operating successfully and efliciently in the face of prior attempts and failure to produce a simpler system than the complex costly two line system, is unexpectedly more responsive and satisfactory in starting time and under operating conditions. The single line system of the invention is less expensive and less time consuming to install or service, and a burner assembly using the single line system has proved to be unexpectedly economical.

It is the object of the invention to provide a novel efficiently operating single line system for preheating and conveying a viscous liquid such as fuel oil from a storage tank or the like to a device for using the liquid such as an oil burner.

A further object is to provide a novel single line system of this type wherein the piping between the tank and the burner or burners is electrically heated with special controls.

A further object of the invention is to provide a single line system of this type wherein the supply line between the tank and burner or burners has a novel air relief arrangement which in the preferred embodiment takes the form of a pipe leading back to the tank.

A further object of the invention is to provide a novel single line system for drawing viscous liquid from a reservoir wherein one end of an electrically heated supply pipe projects into the reservoir and contains an electrical heater adapted to heat the liquid being drawn therethrough and a motor driven pump is provided in the pipe line to deliver the liquid to a utilization device, and an interlock is provided to energize said. heater only when the pump is: being driven by said motor.

A further object of the invention is to provide a fuel oil transporting and preheating system wherein a single electrically heated pipe line is provided between an oil storage tank and a burner assembly with an electric motor driven pump in the pipe line and a suction stub at the tank end of the pipe line projecting into the tank below the normal level of fuel oil therein, and an electric heater element is provided within the suction stub to preheat the surrounding fuel oil, which element may be automatically electrically energized only when the pump motor is energized, and another electrical heater is provided in the pipe line between the pump and the burner assembly for further raising the fuel oil temperature in the pipe line toward the eventual burning temperature in the burner assembly.

A further object of the invention is to provide an electrically heated transportation pipe for viscous liquid oil wherein a pump is provided in the pipe line and provision is made for immediately recirculating liquid from the pump outlet into the pipe line adjacent the pump intake in accord with the varying flow requirements of the oil burner or burners to which the oil is supplied.

A further object of the invention is to provide a novel electrically heated single supply pipe line transporting liquid to at least two devices for using the liquid wherein the system is provided with a sensing leg having the same cooling rate as the pipe section individual to at least that one of the devices which may be inactive part of the time.

Is is a further object to provide a novel single line fuel oil system having special pump arrangements and the elimination of entrained air from the line at the pump outlet.

Further objects will appear as the description proceeds in connection with the appended claims and the annexed drawings wherein:

Figure 1 is a partially diagrammatic and sectional view illustrating a preferred embodiment of the single line system of the invention;

Figure 2 is a schematic wiring diagram of the transformer control circuit; and

Figure 3 is a schematic wiring diagram of the interlock between the pump motor and suction stub heater circuits.

The invention is essentially concerned with supplying a flow of viscous material from a tank or other reservoir to one or more appliances or devices where the material is utilized. In the preferred embodiment of the invention herein illustrated and described, fuel oil is withdrawn from a storage tank 11 and supplied to two oil burner assemblies indicated at 12 and 13, and as far as the invention is concerned there may be any number of oil burner assemblies including only one.

The tank 11 is the usual fuel oil tank which may be buried below the surface of the ground outside the wall 14 of the building containing the boilers or other apparatus using the oil burners 12 and 13. The oil used today in public schools and other buildings and most industrial plants is the relatively viscous type known as Bunker C or No. 6 which flows slowly especially when the tank temperature is about 50 F. as is usually the case most of the year.

Connecting through the top wall of the tank is a hollow suction stub pipe 15 that has an open lower end disposed sufliciently near the bottom of the tank that it is always below the normal oil level in the tank, about eight inches above the bottom of the tank, so that substantially all of the oil may be drawn through it. At the top of pipe 15 outside the tank is a T-coupling 16 disposed with the cross of the T aligned with pipe 15 and the leg 17 extending at right angles for connection to the oil supply pipe 18 for the oil burners.

Pipe 18 comprises an initial section 19 containing a one-way check valve 21 of conventional type for preventing reverse flow of oil toward the tank but freely permitting oil flow toward the burners. Within the build ing a vertical pipe section 22 contains a manual shut off valve 23 and a generally horizontal section 24 that is connected by T-fitting 25 with a pump inlet pipe section 26 having a manual shut off valve 27 for con trolling supply of oil to pump 28.

The pump outlet pipe section 29 contains a manual shut olf valve 31 and is joined by fitting 32 to pipe section 33 which extends up through the bottom of an air separation chamber 34 at 33 and terminates short of the top of that chamber so that oil spouts into the chamber therefrom. Pipe section 35 provides an outlet from the lower end of the air separation chamber 34 and extends to the inlet of a low density electric immersion heater assembly 36. The oil after flowing through heater 36 emerges through pipe section 37 and flows through fitting 38 and pipe section 39 to the oil burner assembly 12. Where two oil burner assemblies are supplied as illustrated, fitting 38 is a T-fitting, and a further pipe section 41 leads to oil burner assembly 13.

A pressure responsive valve 30 is provided in a bypass pipe 40 leading from the lower end of chamber 34 back to pipe section 24 upstream ofthe pump connections, for a purpose to be described.

It will be noted that two pump sets are shown provided in the line, comprising pump 28 and'a pump 42 which is connected in parallel with pump 28 by an inlet pipe section 43 from fitting 25 and an outlet conduit section 44 containing a manual shut off valve 45 and leading to T-fitting 32. One pump set can be cut out while the other operates, or both can operate at the same time.

Each of the oil burner assemblies 12 and 13 comprises an inlet pipe section 46 having a manual shut off valve 47 and a strainer 48 and an outlet pipe section 49 containing a oneway check valve 51 that does not permit oil to reverse flow from fitting 52 through pipe section 49.

The air separation chamber 34 is a simple strong walled receptacle into which the oil is pumped through pipe end 33. The oil spills over the end of pipe 33 and tends to move to the bottom of chamber 34 where the outlet pipe section 35 and bypass pipe 40 are con nected. Chamber 34 is full of oil normally.

A pipe section 54 of relatively small diameter extends from the top of chamber 34 and contains an adjustable air bleed valve 55. Conduit section 54 is connected to a larger diameter pipe section 56 which extends through the building wall to terminate in a pipe section 57 that opens through the top Wall of the tank to discharge into the space above the oil level in the tank.

Emergency relief valves 58 and 59 are provided in the respective pump outlets and are connected by a pipe section 61 to a bypass pipe section 62 which discharges into the pipe section 56. Valves 58 and 59 are conventional normally closed pressure responsive valves that open only when the oil pressure increases, as caused by a line blockage at the burner, to a predetermined amount and then they act to relieve the system by bypassing the oil from either or both pump outlets to the pipe section 56 for return to the tank.

For standby heating of oil in the pipe line between the tank 11 and the oil burners, the oil carrying pipm are heated by passing an electric current therealong. These pipe sections are all of electrically conductive material, preferably cast iron or steel, and they have a certain amount of electrical resistance to passage of electric current. The heat generated in the pipe walls is, according to known laws of electricity proportional to the square of the current and the pipe resistance (I R), and this provides uniform surface heating internally of the pipe surrounding the oil stream therein whereby friction between the pipe and the rather sluggish oil is greatly reduced and flow starting and maintenance is made easy.

The immediate source of power for energizing the electrically conductive piping outside the tank 11 is a transformer 65 having a variable tap primary 66 connected to a suitable switching arrangement in a control panel box 67, and one side of the usual 220 volt input line is connected into the control panel box 67 through a master switch 68. The variable tap primary gives a selection of output voltages.

The transformer secondary 69 is connected by leads to opposite sides of an insulated flange pipe coupling 70 in the pipe section 35. This coupling consists essentially of metal flanges A and B rigidly secured together with an electrically insulating gasket C between them so that A and B and the metal pipes connected thereto on opposite sides of the coupling are electrically isolated from each other. The coupling 70 may have any desired mechanical configuration and embody suitably insulated bolts or like fasteners between the flanges. The transformer is a step down transformer which produces a voltage in the-range of 12-20 volts across the secondary 69 according to the setting of the primary tap, and this low voltage is not only relatively harmless to accidental contact but it enables relatively high currents in the neighborhood of 300500 amperes to be supplied to the pipe walls to be heated.

Couplings 7182 are provided at various points in the system and these are preferably identical with coupling 70, each having metal pipe flanges A and B electrically insulated by a gasket C. In the embodiment of the invention supplying oil to more than one oil burner assembly, a sensing leg pipe section 83 coupled at its open upper end into pipe section 35 and closed at its lower end by coupling 82 is provided for a purpose to appear.

Starting clockwise from coupling flange 7013 which is connected to one side of the transformer secondary, the pipe heating electrical circuit comprises pipe section 35 to the right of coupling 70, the metal housing of immersion heater 36 which is eflectively part of the pipe line, pipe section 37 up to flange 71A, pipe section 39, pipe section 49 up to flange 73B, jumper wire 87 to flange 74B, pipe section 46 to flange 72B, jumper wire 88 to flange 71B, pipe section 41 to flange 75A, pipe section 49 to flange 76A, jumper wire 89 to flange 77A, pipe section 46 to flange 75B, long jumper wire 90 to flange A, pipe section 56 to flange 78A, jumper wire 91 to flange 79A, pipe sections 19, 22, 24, the metal pump parts and piping connections through pipe section 33, metal chamber wall 34, pipe section 35 to flange 81B, sensing leg 83, flange 82A, jumper wire 92 to flange 81A and the intervening part of pipe section v35 to flange 70A which is connected to the other side of transformer secondary 69. This is an uninterrupted circuit that is energized to heat the pipes whenever the transformer 65 is energized. Where only one oil burner ils 1igncluded the jumper 90 would be attached to flange A thermostat bulb unit the projecting end of which is shown at 93 is inserted through coupling 82 into the lower end of sensingleg 83 and connected by its usual cable to the adjustable temperature indicator and switch assembly 94, and this switch assembly is connected by wiring in conduit 95 into the control box to control the energization of the transformer primary as will appear.

The electrical heater 36 is of the so-called immersion type and is essentially a hollow metal tube 96 larger than the conduits 35 and 37 and through which the oil passes in contact with end mounted electrical heater elements such as indicated at 97. Each set of elements 97 is separately energized by current from the main lines passing through a normally closed disconnect switch 98 and an adjustable resistance unit 99 having a resistance control dial at 101 for selecting the temperature to be imparted to the oil. ciatcd mountings and control at 99 are preferably mounted on outer flanges 84 and 85 so that the circuits may be electrically separate at this region.

Mounted on the upper end of the suction stub is a low density heater assembly comprising a waterproof base 102 secured upon a flange 100 to serve as a closure for the upper end of the fitting 16 and having a liquid tight heater element 103 projecting down the interior of the suction stub 103. This element contains internal heater wires that are electrically connected through body 102 and electrical conduit 104 to a contactor control unit 105 which is essentially a switch in the circuit to the heater element 103 automatically actuated to close only when the electric motor for one or the other of the pumps 28 or 42 is energized, so that the heater element 103 is energized only when pump suction is being exerted to withdraw oil from the tank 11. A thermostatic switch is also provided in base 102 to break the circuit for heater 103 whenever the oil within the upper end of the suction stub reaches a predetermined value, usually about 120 F. The suction stub heater is energized through an independent circuit coming through a manual disconnect switch at 106.

Thus the electrical controls derive energy from three independent circuits. First, the pipe wall heating circuit having its input controlled by switch 68, secondly the immersion heater 36 circuit having its input controlled by switches 98, and thirdly the suction stub heater having its input controlled by switch 106.

Figure 2 diagrammatically shows the control of pipe wall heating by the thermostat which is responsive to the line fluid temperature in the sensing leg 86. Switch 107 of the thermostat is normally closed and this energizes solenoid coil 108 to close normally open switch 109 and thereby complete the circuit through lines 111 to the transformer primary. In practice the thermostat switch at 107 is set to be open for oil temperatures above a limit in the range of 100 to 125, the particular limit being selected to suit operating conditions, and to be closed when the oil temperature drops below that limit. When switch 107 opens switch 109 automatically opens. Thus when master switch 68 is closed the control ofv pipe Wall heating becomes automatic.

Figure 3 shows diagrammatically the interlock between the circuits of suction stub heater element 103 and the pumps. Heater element 103 cannot be energized unless the motor circuit is closed. When switch 106 is closed the pump motor 28M circuit is energized to start oil withdrawal from the tank 11. It will be noted that an individual normally closed switch 113 is provided to shut down the motor if desired. A solenoid coil 115 is disposed in parallel with the pump circuit and this immediately closes solenoid switch 116 to energize the heater coils 117 within liquid tight metal heater 103. The normally closed temperature responsive thermostatic The heater elements 97 and asso Operation Start of the operation will assume that the oil burners have been inactivated for some time and the pipe line 18 contains only unheated oil. The operator first closes switch 68. This immediately activates the transformer 65 to start heating the oil supply pipe line. The power available through transformer 65 is preferably enough to heat the oil standing in the pipe lines to about l00120 F. Where the building is shut down only over a weekend or a few days, switch 68 is usually left closed to keep the oil pipes hot automatically on standby operation. Switches 98 are closed to activate the heater 36.

Switch 106 is closed to activate the suction stub heater circuit but that circuit is not yet energized because of normally open switch 116.

The burner assemblies 12 and 13 are activated in the usual manner by controls not shown, which may be the building room control thermostats, and now the pump starts to deliver oil to the burners. This is initiated by closing switch 106 whereby the electric motor for pump 28 is energized and suction is developed in pipe sections 24, 22, 19 andstub 15. Normally pump 42 is inactive but ready to operate when pump 28 is shut down. An interlock between the burner controls and pump switch 106 may be provided. The circuit to heater coils 117 is currently completed when switch 116 automatically closes, and heater 103 starts to heat the column of oil within tube 15, thereby making it easier to draw the normally stiff viscous 50 F. oil out of the tank 11.

The oil passing through supply line 18 is eventually pumped under pump pressure through pipe section 33 into the chamber 34. There entrained air may leave the cascading oil and cut through the small adjustable bleed valve 55 into the pipe 56 and discharge into the upper tank space. It will be noted that the pipe 33' brings the oil up to the top of chamber 34 and allows it to drop toward the bottom connection of outlet pipe section 35. Any air bubbles or pockets entrainedin the oil will separate from the oil which otherwise substantially fills chamber 34, and the air rises upwardly into the open end of pipe 54. It is possible and even probable that a small amount of oil mist is carried along with the discharged air but it is recovered when dumped back'into the'tank 11.

A column of oilcollects in the heated sensing leg pipe 86. The sole function of this sensing leg is to provide a length of pipe which is substantially equal in heat loss characteristics, when the transformer 65 is not energized, to the length of pipe 41 leading from fitting 38 to burner assembly 13. Thus if the burner assembly 13 should be inactive over a long period the stationary oil within pipe 41 beyond T-fitting 38 will tend to cool and become sluggish. At the same time sensing leg 86 is cooling oft" at the same rate, and when the temperature of the oil in sensing leg 86 reaches the set lower limit of say 120 F. the thermostat acts, independently and regardless of the fact that the temperature of the oil in pipe sections 18, 35, 37' and 39 may be higher than 120 F., to energize the transformer 65. This electrically heats the entire pipe line including sensing leg 86 and the cooling pipe 41 and the result is that the oil in pipe 41 is always kept at the desired pumpable 120 F. temperature ready to flow should the associated oil burner 13 be activated. The oil'in pipe 41 heats up at the same rate as that in sensing leg 86.

As the oil flows through immersion heater 36 it is raised to the burning temperature desired at the oil burners. This is quite advantageous in that it facilitates quick starting and good combustion in the oil burners. The moving oil rate is so correlated to the heat output at tion 37 has a temperature in the range of approXimately 160 F. to 200 F., the desired temperature being selected by the adjustment at 101.

Now the heated oil descends pipe sections 39 and 41 and enters the burners through pipe sections 46. Any oil in excess of the burning rate is delivered back through pipe section 49 where it joins the descending hot oil. Thislirnited recirculation at each burner of course gauges the amount of oil that descends the pipes 39 and 41.

It will be noted that there is no return of hot oil to or into the tank 11, and in operation only the exact amount of oil that is being burned is currently withdrawn from tank '11. Since this oil ascending suction stub 15 is moving only at the speed necessary to satisfy the burning rate at the oil burner or oil burners, the system efiiciently draws relatively cold tank oil into the open lower end of suction stub 15. Prior to the invention it was considered necessary to withdraw oil from the tank in excess, about double, of the burning rate and return the hot oil to the inlet end of the suction pipe so as to liquify the viscous cold tank oil. This wasteful practice has been eliminated by the present invention.

One of the reasons for drawing excess oil out of the tank was to keep the line pumps primed, and single line systems have been hitherto considered unworkable because of the tendency of entrained air to accumulate in the pumps and produce air locks in the usual pumps at the burners. This difficulty is not encountered in the present invention wherein the entrained air is bled 01f through valve 55 and only a continuous flow of oil is pumped to the burners.

Should the oil line become blocked anywhere at the output sides of the pumps 28 and 42, the oil from the pump outlets will bypass entirely through valves 58 and 59 and pipe sections 61 and 62 into pipe 56 which is of sufficient size to handle the pumping rate and return all of the pumped oil back into the top of the tank as an emergency condition to prevent rupture of the lines. Pipe section 56 is of about the same size as the sections of pipe line 18 so as to have the same electrical resistance and serve as a conductor. The air bleed valve 55 has such a small orifice that in event of the emergency bypass through pipe 62 no oil will flow into chamber 34 from pipe 56.

When, in a two burner system like that of Figure 1, one burner is shut down and the full pump capacity is delivered to pipe section 33, that part of the pumped oil not required by the inactivated burner is locally recirculated through pressure responsive valve 30 and pipe section 40 back into the suction line 24 where it joins the oil coming from the tank 11 to enter the pumps. The valve 30 is opened by the back pressure of the oil built up in chamber 34. Thus pump 28 normally pumps enough oil to satisfy both burners 12 and 13 but if one is shut down or if the burning rate either is low the oil not demanded by pipe 35 will be recirculated at the pump, and only enough oil to satisfy the burning requirements passes through pipe section 22.

As above explained heater element 103 is electrically heated only when the oil is being pumped. This prevents excess oil temperatures in the suction stub. A further control of this oil temperature in the suction s'tub is af-' forded by the thermostat switch 118 which will deenergize the coils 117 when the oil temperature in the suction stub exceeds the desired pumpable temperature of say 120 F. even when the pump is operating as on low burner use. The temperature of the oil in the suction stub is purposely not allowed to rise above 120 F. or so because if heated above that point some of the oil would vaporize under the existing pump vacuum and cause vapor lock in the oil pump, thereby causing pumping failure. When heater is set to produce 120 F. oil in the stub 15 with oil rising through it at the rate required to satisfy two burners, should one burner cut off as in warm weather, the slower moving oil in the suction stub will tend to be hotter and the thermostat switch at 118 takes 8 care of this event. Since the oil downstream of the pump is at pump pressure it is possible to attain the and above temperature without vaporization. Thus the invention provides a single line system having two stage 7 pumpingand two oil temperature operation.

. The essential advantages of the novel single line sys tem over the hitherto standard two line system that it replaces are that less piping and smaller pipe sizes are used since only the amount of oil that is to be burned is steadily withdrawn from the tank, the pump is smaller, the transformer capacity is smaller since less and smaller piping is to be heated, labor and parts costs are lower and installation and operation are more economical and efficient.

A major advantage of the single line system over the old two line systems is that the single line system eliminates the return of excess hot oil to the tank or the suction line of the pump which would tend to overheat and vaporize the oil at the suction side of the pump, a condition which could readily arise when one burner of a multiple burner installation operates alone or when all burners are operating at a low firing or oil consumption rate and large quantities of excess hot oil are returned.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States Letters Patent is:

1. In a system for heating and transporting a viscous material from a reservoir to a device that uses the material, an electrically heated pipe line extending between the reservoir and device, means in the reservoir for heating the material at the inlet of said pipe line, a pump in the pipe line for withdrawing said material from the reservoir and forcing it through the pipe line, and control means for energizing said heating means only when said pump is operating.

2. In the system defined in claim 1, means responsive to the temperature of the heated material in the reservoir and actuated whenever that temperature exceeds a preline extending between the tank and the burner, a pump in said line for withdrawing the fuel from the tank and supplying it to the burner, an electric motor for driving said pump, said pipe line extending into said tank and terminating in an open end below the normal 'level of fuel in the tank, an electric heater within the said pipe line to heat the fuel adjacent said open end, an electric circuit for energizing said pump motor, an electric circuit for energizing said heater, and control means interlocking said circuits so that said electric heater may be energized only when said pump motor is energized. I

4. In a system for transporting viscous liquid fuel from a storage tank to a burner, an electrically heated supply pipe line extending between the tank and the burner, a pump in said line for withdrawing the fuel from the tank and supplying it to the burner, an electric motor for driving said pump, a suction stub pipe constituting an effective continuation of said pipe line extending into said tank and terminating in an open end below the normal level of fuel in the tank, an electric heater element within the suction stub pipe, an electric circuit for energizing 5. In a system for transporting viscous liquid fuel from a storage tank to a burner, a supply pipe line extending between the tank and the burner, means for electrically heating the pipe walls, means for controlling energization of said heating means for regulating the oil temperature in said pipe line, a pump in said line for withdrawing the fuel from the tank and supplying it to the burner, an electric motor for driving said pump, a suction stub pipe constituting an effective continuation of said pipeline extending into said tank and terminating in an open end below the normal level of fuel in the tank, an electric heater element extending within the suction stub pipe so as to heat the fuel within the suction stub pipe, an electric circuit for energizing said pump motor, an electric circuit for energizing said heater element, and control means interlocking said circuits so that said electric heater may be energized only when said pump motor is energized.

6. In a system for heating and transporting viscous liquid fuel from a storage tank to a burner, a supply pipe line extending between the tank and the burner, means for electrically heating said pipe line, an electric heater in said pipe line near the burner for materially raising the temperature of the fuel about to enter the burner, means comprising a thermostat in the pipe line upstream of said electric heater for controlling energization of said pipe line, a pump in said line for withdrawing the fuel from the tank and supplying it to the burner, an electric motor for driving said pump, a suction stub pipe constituting an effective continuation of said pipe line extending into said tank and terminating in an open end below the normal level of fuel in the tank, an electric heater element extending within the suction stub pipe so as to heat the fuel within the suction stub pipe, an elec tric circuit for energizing said pump motor, an electric circuit for energizing said heater element, and control means interlocking said circuits so that said electric heater may be energized only when said pump motor is energized and liquid fuel is being pumped out of said tank.

7. In a system for heating and transporting viscous liquid fuel from a storage tank to a burner, a supply pipe line extending between the tank and the burner, means for electrically heating said pipe line, a motor driven pump in said line for withdrawing the fuel from the tank and moving it toward the burner, a suction stub pipe constituting an effective continuation of said pipe line extending into said tank and terminating in an open end below the normal level of fuel in the tank, a heater within the suction stub pipe, and means for energizing said heater only when said pump is in action.

8. In a single line system for conveying viscous liquid from a reservoir to a device that uses the liquid, a supply pipe line extending from the tank to the burner, means for heating the liquid during passage through said pipe line, a pump in said pipe line, and means defining an air separation chamber in said pipe line downstream of said pump having inlet and outlet connections to the adjacent pipe sections and having an air bleed outlet.

9. In a single line system for conveying viscous liquid fuel from a tank to a burner, a supply pipe line extending from the tank to the burner, means for heating the fuel during passage through said pipe line, a pump in said pipe line, means defining an enlarged chamber in said pipe line downstream of said pump, and means providing a gas discharge outlet for said chamber.

10. In a single line system for conveying viscous liquid fuel from a tank to a burner, a supply pipe line extending from the tank to the burner, means for heating the fuel during passage through said pipe line, a pump in said pipe line, means defining an enlarged chamber in said pipe line downstream of said pump, and means providing an vair exhaust passage from said chamber to said tank.

11. In the system defined in claim 10, said exhaust passage comprising a pipe connected between said chamber and said tank and having a restricted gas bleed valve.

12. In the system defined in claim 11, an emergency bypass conduit connected to the pump outlet and to said exhaust passage pipe between the tank and said valve.

13. In a single line system for conveying viscous liquid from a reservoir to a device for using the liquid, a supply pipe line extending from the reservoir to the device, means for heating the liquid passing through the pipe line, a pumpin said pipe line, and means responsive to the quantity of said liquid used by said device for automatically bypassing some pumped liquid from adjacent the'pump outlet back into said pipe line upstream of said pump.

14. In a single line system for conveying viscous liquid fuel from a tank to a burner, a supply pipe line extending from the tank to the burner, means for heating the fuel passing through the pipe line, a pump in said pipe line, and means in said pipe line downstream of said pump responsive to the fuel demands of said burner for automatically bypassing excess pumped fuel back into the pipe line upstream of said pump.

15. In a single line system for conveying viscous liquid fuel from a tank to a burner, a supply pipe line extending from the tank to the burner, means for heating the fuel during passage through said pipe line, a pump in said pipe line, and means defining an enlarged chamber in said pipe line downstream of said pump, and a bypass connection between said chamber and the pipe line upstream of the pump.

16. In a single line system for conveying viscous liquid fuel from a tank to a burner, a supply pipe line extending from the tank to the burner, means for heating the fuel passing through the pipe line, a pump in said pipe line, and means in said pipe line downstream of said pump responsive to the fuel demands of said burner for automatically bypassing excess pumped fuel back into the pipe line upstream of said pump comprising an enlarged portion of said pipe line downstream of the pump defining a chamber, a conduit connecting said chamber to said pipe line upstream of the pump, and a regulating valve for said conduit responsive to the liquid pressure in said chamber.

17. In a single line system for conveying viscous liquid fuel from a tank to a burner, a supply pipe line extending from the tank to the burner, means for heating the fuel passing through the pipe line, a pump in said pipe line, and pressure responsive means in said pipe line downstream of said pump for automatically bypassing the pumped fuel back into said tank when the pipe line pressure downstream of the tank exceeds a predetermined amount.

18. In a single line system for transporting viscous liquid fuel from a storage tank to a burner, a supply pipe line of electrically conductive material extending between the tank and the burner, a pump in said line for withdrawing the fuel from the tank and supplying it to the burner, an electric motor for driving said pump, electric power means including a transformer for supplying low voltage-high current power to heat said pipe line by passing the electric current through the pipe walls, a suction stub pipe constituting an effective continuation of said pipe line extending into said tank and terminating in an open end below the normal level of fuel in the tank, an electric heater element extending within the suction lstub pipe so as to heat the fuel enclosed by and passing through the suction stub pipe, a liquid fuel heater in said supply line between the pump and said burner for further raising the temperature of the fuel substantially to its burning temperature for quick combustion at the fuel burner, an electric circuit for energizing said motor, an electric circuit for energizing said suction stub heater element, and control means interlocking said circuits so that the electric heater element in said suction stub pipe may be energized only when said pump motor is energized and liquid fuel is being pumped out of the tank.

19. In a system for transporting viscous liquid fuel from a storage tank to at least two burners, a supply pipe line of electrically conductive material extending between the tank and one burner and having an electrically conductive pipe extension for supplying fuel to the second burner, electric power means including a transformer for supplying low voltage-high current power to heat said pipe line including said extension by passing the electric current through the pipe walls, said pipe line having a closed outer end branch leg disposed upstream of said one burner, and a thermostat responsive to the temperature 10 said leg is below a predetermined degree, said leg and said extension being of such relative size as to have substantially the same heat loss when cooling.

References Cited in the file of this patent UNITED STATES PATENTS 1,617,470 Williams Feb. 15, 1927 2,224,403 Lines Dec. 10, 1940 1 2,368,164 Schumann et al. Jan. 30, 1945 FOREIGN PATENTS 478,449 Great Britain Ian. 19, 1938 

